A fan wheel is described in various versions in the publication JP 2001-263 294. In this case, the shroud or the baseplate or each of the two is to have a contour stepped obliquely in the circumferential direction. As a result of this step shape oblique in the direction of rotation, a tendency of the flow to break away is to be reduced and the noise and efficiency are thereby to be influenced positively. The result of the step shape is that each fan blade has different (axially measured) outlet widths on its suction side and on its delivery side, specifically, depending on the embodiment, the outlet width on the suction side may be smaller or greater than the outlet width on the delivery side.
EP 1 933 039 A1 describes a radial fan with ribs, clearances or indentations on the outside of the shroud. This configuration is to lead to a noise reduction as a result of a specific flow routing.
The further publication EP 1 032 766 B1 describes a fan wheel, in particular for a turbocharger. In this fan wheel, blades are formed by embossings on at least one of the two disks (baseplate and/or shroud). These embossings likewise give rise to a nonrotationally symmetrical geometry. However, this publication is not concerned with influencing the flow, but mainly contains manufacture-related and stability-promoting aspects.
Numerous further publications describe rotationally symmetrical fan wheels. Mention may be made here, merely by way of example, of the publications DE 29 40 773 A1, DE 199 18 085 A1, EP 1 574 716 B1 and DE 203 03 443 U1. Such fans with rotationally symmetrically designed baseplates and/or shrouds have, both in the direction of the axis of rotation and in the circumferential direction, in part, highly nonuniform velocity and pressure distributions, that is to say locally elevated velocity/pressure ranges. This may lead to flow breakaways and even backflows which, in turn, cause aerodynamic losses, losses of efficiency and also an increase in noise emission.